Absorbent structures are known for inclusion in disposable absorbent articles used for absorbing body fluids and other exudates. Such absorbent structures have traditionally been made from readily available and relatively inexpensive materials such as cotton fibers, wood pulp fluff, cellulosic tissue or wadding, or other absorbent fibers. These materials have provided satisfactory absorbency of fluids both in terms of absorbency rate and overall absorbent capacity. Unfortunately, absorbent structures made from such materials may tend to collapse when wetted, thereby losing some of their void volume. Such structures may also allow absorbed fluid to be squeezed back out of the structure onto the user of the absorbent article. Furthermore, when such structures have absorbed fluid, they may present an uncomfortable wet feeling against the skin of the user.
More recently, superabsorbent polymer particles have been combined with the more traditional absorbent materials to provide structures with enhanced absorbency and retention, which may help to eliminate the problems of squeeze-out and wet surface feel. Replacement of traditional absorbent materials with superabsorbent polymer particles may also allow for absorbent products to be thinner while retaining the absorbent capacity of thicker, bulkier products. A drawback to superabsorbent polymer particles, however, is their relatively high cost compared to the more traditional absorbent materials.
Additionally, since superabsorbent polymer particles tend to swell as they absorb fluid, they may cause what is commonly known as gel-blocking. In other words, as fluid is absorbed by the particles of superabsorbent polymer, those particles swell and may form an occlusive layer of swollen superabsorbent particles. This occlusive layer then prevents the passage of additional fluid into the structure. Thus, the superabsorbent polymer particles must be properly placed within an absorbent structure to allow for this swelling and to most fully utilize their absorbent capacity. Generally, prevention of gel-blocking has been realized by mixing superabsorbent polymer particles with spacer materials, such as absorbent or nonabsorbent fibers, or by placing the superabsorbent polymer particles toward the bottom of the absorbent structure. However, although these methods of superabsorbent polymer placement may minimize gel-blocking, they do not effect the most efficient use of the superabsorbent polymer's absorbent capacity.
It may often be desirable to add other particulate or powder materials to absorbent structures to provide such benefits as odor control, enhanced dryness, skin protection or treatment, or a clean appearance. Examples of such particulate or powder materials include, without limitation, zeolites, sodium bicarbonate, microencapsulated perfumes and other compounds, titanium dioxide, and absorbent or superabsorbent fibers. Unfortunately, most of these types of particulate materials are higher in cost than traditional absorbent materials, and therefore, it is desired to accurately place precise amounts of these particulate materials within the article so that they are fully utilized with minimum waste and minimum cost.
Therefore, what is needed is an absorbent structure with good absorbency and retention of fluid. What is also needed is an absorbent structure which will help to provide a dry feel to the skin of a user when used in an absorbent article. What is further needed is an absorbent structure with superabsorbent polymer particles or other particulate materials spaced and placed within the structure to most fully utilize the unique capabilities of particles, and a method and apparatus for making such an absorbent structure.